The important relationship of diet and nutrition in the development of cancer has become well known through various research efforts. Laboratory studies have shown cancer inhibitory function for various natural and synthetic nutrients in various models, which have been corroborated by human epidemiologic studies of nutrient intake, tissue levels, and cancer incidence. Vitamin A, beta- carotene, and selenium have been strongly implicated for their cancer preventive potential, with sufficient evidence for these substances to warrant their use in prevention trials. In addition, the roles of other nutrients in cancer cause and prevention (e.g., dietary fats and fiber) require further investigation. The objectives of this cooperative project with the government of Finland are: 1) to determine if either beta-carotene or alpha- tocopherol supplement is effective in preventing lung cancer in smokers; 2) to better assess the role of fats, selenium, and vitamins A, E, and C in breast cancer development; and 3) to evaluate the relation of intake of various nutrients to subsequent cancer. The project includes three studies. The first is a 5- year, randomized, double-blind, placebo-controlled, 2x2 factorial prevention trial of daily beta-carotene (10 mg daily) and alpha- tocopherol (50 mg daily) among smokers at high risk for lung cancer. The difference in lung cancer incidence between intervention groups will be determined. The second is a breast cancer case control study of fats, total calories, selenium, and vitamins A, E, and C. The role of various anthropometric measurements as well as genetic markers for breast cancer will be explored. The third project will be a comparison of nutrient intakes in cases and reference subjects identified from an existing large cohort with prediagnostic baseline dietary histories. Associations between various dietary components and several cancers will be assessed. Several pilot studies have been completed to date, and the prevention trial and breast cancer study are underway.